As seen in the September, 1998 issue of 73 Amateur Radio Today Magazine

The NHRC-4 is an inexpensive linking repeater controller. The controller
has a "primary" and a "secondary" radio port. The
primary port is used for the controlling repeater, and the secondary port
can be used for a remote base, link radio, or "slaved" repeater.
Unique courtesy tones provide feedback of the input source and link state.

The controller is programmable by sending DTMF sequences. The CW ID, hang
time, ID timer, timeout timer and tail message counter can all be
programmed by the user. All programming is password-protected, and is
stored in non-volatile EEPROM memory.

The NHRC-4 has very low power consumption--less than 20 mA with the
LEDs disabled--making it ideal for use in a solar-powered repeater.

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Features:

Easily integrates with any repeater.

Secondary port can be remote base, link radio or slaved duplex repeater.